Sound-reproducing mechanism



June 17, 1930. P. A. ROBBINS 1,754,120

SOUND REPRODUCING MECHANISM Filed May 20, 1929 7%]. E LWE 'INVEN'TDRQPatented June 1,7, 1930 UNITE STATES- PATENT OFFICE PERCY A. ROBBINS, OFHIGHLAND PARK, ILLINOIS souma nnrnonucme MECHANISM A1ip1icat ion filedMay 20,

I attain my object by utilizing for thesound trace a coating ofbismuthwhich may be applied in any convenient manner, as, for example,in t e form. of a self-drying paste or suspension Which;will ;produce aneven coating when dry. The bismuth is hightly diamagnetic and the soundrecord so produced will when drawn through a magnetic field, soinfluence the field as to produce electro-magnetic disturbances whichmay be utilized'to reproduce as sound the "ariati'ons of the sound traceon the record. A record such as described may be used in connection withmany different forms of electro-magnetic mechanism. I describe for thatpurpose two forms as shown in the accompanyi'ng drawings in which I Fig.1 is a cross section, partly in elevation, of one form of theapparatus;-

Fig. 2 a side elvation of a' modified form of the apparatus; and 1 iFig. 3 a plan viewof a flexible strip with a soundtrace formed thereonin accordance .with my invention, 85- 1 is the sound record which beformed of celluloid and which will, when .theapparatus is used inreproducing "sound in connection with moving pictures, bear the usualseries of pictures thereon. 2 isthe sound trace. formed on the stripby'the apphcatlon of a coating of bismuth thereto,

will usually 1929. Serial No. 364,548.

sound trace passes through the magnetic field its varying width andposition cause fluctuationsand disturbances in the flux flow and thesevariations in the field induce undulating currents of electricity in thecoil.

In Fig. 2 a similar arrangement of the strip and electro-magnet isshown, but for the coil 4 there is substituted an armature 5 suspendedfrom a stationary support .6"

in a state of stable equilibrium; This armature carries a mirror 7. Thevariations .in v

the positions of the lines of 'force in the magnetic field willnecessarilyvibrate the armature and thus cause a beam of light from asource 8 to be directed towards. a

light-sensitive cell 9 included in an electric circuit. Variations ofthe illumination of the l-ight-s'ensitive'celldue to the vibrations ofthe mirror will thus'cause an undulatory current to flow in the circuitof the light sensitive cell, which current may be suitably amplified andconverted into sound waves.

The sound trace 2 may have any form known to the art.

What I claim is:

1. A sound record formedas a fleicible" strip having a sound traceformed thereon of a highly diamagnetic material.

2. A sound record formed as afiexiblc strip having a sound trace formedthereon of bismuth.

. 3. A sound record having a sound trace formed thereon of a materialhighly diaina netic relative to the body of therecord.

signed at Highland Park, 111. this 8th day of May, 1929. a. PERCYROBBINS.

as hereinbefore referred to. Beneath the 7 sound record strip is locatedan electro-magy '45 ing one side located close to the strip 1 so as tolie within the magnetic field produced net 3. Above the film -'I show acoiht havby the magnet 3. The turns of the coil may be crossways of thestrip as shown or they e diamagne'tic

